Physical development systems, processes and related materials

ABSTRACT

This disclosure relates to a new and useful complex of silver ion with nitrilotriacetate ions which is particularly useful in sensitizing a photographic latent image on a photosensitive medium especially those in which the photosensitive component is a photoconductor. The complex can be applied to the photoexposed medium or formed on the medium before or during photoprocessing. Also described are methods of photoprocessing latent photographic images, especially by amplifying latent silver images with nonsilver metals such as copper and tin.

United States Patent Mowat Feb. 29, 1972 [54] PHYSICAL DEVELOPMENTSYSTEMS, 3,256,092 6/1966 Means et al...'. ..96/60 PROCESSES AND RELATED3,458,316 7/1969 Viro ..96/94 MATERIALS Inventor: Lois E. Mowat,Waltham, Mass.

Assignee: ltek Corporation, Lexington, Mass.

Filed: July 11, 1968 Appl. No.: 743,983

Shepard et al. ..96/60 Primary Examiner-Norman G. Torchin AssistantExaminerJohn L. Goodrow Att0rney-Homer 0. Blair, Robert L. Nathans andW. Gary Goodson [5 7] ABSTRACT This disclosure relates to a new anduseful complex of silver ion with nitrilotriacetate ions which isparticularly useful in sensitizing a photographic latent image on aphotosensitive medium especially those in which the photosensitivecomponent is a photoconductor. The complex can be applied to thephotoexposed medium or formed on the medium before or duringphotoprocessing. Also described are methods of photoprocessing latentphotographic images, especially by amplifying latent silver images withnonsilver metals such as copper and tin.

8 Claims, No Drawings PHYSICAL DEVELOPMENT SYSTEMS, PROCESSES ANDRELATED MATERIALS BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to a photographic physical developer and systemsincluding the new developer.

2. Description of the Prior Art Physical development is a photographicdevelopment process distinguished from chemical development by the factthat metal required for contrast formation is largely supplied from thedeveloper system whereas, in chemical development, the contrast metal ispresent as metal ions in the crystal lattice of the grains on the film.Physical development is primarily used for development of latent imagesformed by light-activation of the photosensitive component of aphotographic medium. In general, the physical development can beaccomplished by contacting the latent image with the physical developer,e.g., a solution of reducible metal ion such as silver, mercury, gold,platinum or copper ions and a solution of a reducing agent for theselected metal ion, or, if desired, a latent metal image can be firstformed by contacting the latent image with a solution of sensitizingions, e.g., silver, followed by treatment with additional metal ions anda reducing agent therefor. The additional metal ions need not be thesame as the sensitizing metal ions and when they differ the developmentis known as amplification since the metal latent image, i.e., germ metalimage, is amplified, i.e., intensified, with the second metal. Thislatter process is of particular importance when the second metal isother than silver, a costly component of physical developer systems, butnevertheless an especially effective component, particularly in formingthe latent metal image. Although many metals can be used for formationof the latent metal image in physical development, e.g., copper, gold,platinum, mercury, copper and the like, silver is at present thepreferred metal. Particularly effective amplifying metals are silver,copper and tin, the latter two being preferred since they are moreeconomical than silver but comparable in their action and effect.

Various literature articles and patents are available for description ofthe variety and types of photographic media with which physicaldevelopment is employed to produce visible images corresponding tolatent photographic images on the media. For example, U.S. Pat. Nos.2,057,016; 2,750,292; 2,735,773; 2,183,447; and 3,072,542 describe theuse of various physical developer systems used for image formation withvarious photosensitive media.

British Specification 1,043,250, describes physical developer systemsfor developing latent images on photosensitive media comprising aphotoconductor, especially metal containing photoconductors, which arerendered chemically reducing when exposed to activating 7 radiation,especially titanium dioxide.

One of the basic problems encountered in using physical developers isthe efficiency of germ metal image site formation. The activation of thephotosensitive component of the photographic media results in productionof a number of sites of activation but, up to now, the conversion ofthese activation sites to a corresponding number of germ metal sites hasfallen to considerably less than 100 percent efficiency for reasonswhich do not lend themselves to simple explanation. Thus, when physicaldevelopers are used, the initial photographic media appear to have avery low photographic speed whereas they can have high photographicspeed but, due to the low efficiency of physical development, such highphotographic speed is not apparent.

SUMMARY OF THE INVENTION cially nitrilotriacetate ions, a new silver ioncomplex. In addition to the improvements realized with the new silvercomplex, it hasalso been surprisingly found that silver ion, in the formof the complex, can be employed at concentrations considerably lowerthan concentrations normal to silver ion sensitizing of the prior art.

The silver ion complex, or either component thereof, can be applied tothe photographic medium as such before or after photoexposure, or can beformed in situ by contacting the medium with a source of silver ions anda source of nitrilotriacetate ions, in whatever order. The source ofnitrilotriacetate ions can be the developer of the amplifying solution.There is no limitation to the manner of application of the complex,whether as the complex or formed in situ on the latent image, exceptthat the complex be available when the visible image formation takesplace. In general, the improvements described hereinafter are realizedby converting the photographic latent image to a laten silver image bycontacting with silver ions in the presence of nitrilotriacetateions.The resulting latent silver image can be amplified by any of theart-recognized procedures by use of physical development procedures, toobtain visible images corresponding to the original photographic latentimage.

Particularly effectivein the important step of forming the latent silverimage is a solution of the new silver complex of this invention whichmerely need be contacted with the photographic latent image to obtainthe latent silver image. Also useful are photographic media whichcontain a source of nitrilotriacetate ions with, or without, a source ofsilver ions image when the silver complex is activated as describedhereinafter.

A particularly effective method of amplification of the latent silverimage involves the use of copper or tin amplification processesdescribed in commonly assigned copending U.S. application Ser. Nos.743,981 filed July 11, 1968 and 743,982 filed July 11, 1968,respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention isparticularly effective with photographic media the photosensitivecomponent of which comprises a photoconductor which includes bothorganic and inorganic compounds and mixture of compounds. Preferredphotoconductors are inorganic compounds such as compounds of a metal anda nonmetallic element of Group VIA of the Periodic Table (*PeriodicTable from Langes HAND- BOOK OF CHEMISTRY,9th Edition, pp. 56-57, 1956.)for example, metal oxides, such as zinc oxide, titanium dioxide,antimony trioxide, aluminum oxide, zirconium dioxide, germanium dioxide,indium, stannic oxide, barium titanate, lead oxide, tantalum oxide, andtellerium oxide; metal sulfides such as cadmium sulfide, zinc sulfideand stannic sulfide; and metal selenides, such as cadmium selenide.Metal oxides are generally preferred, and, of these titanium dioxide,because of the unusually good results obtained therewith.

A simple test useful in determining whether a selected material has aphotoconductor effect involves mixing the test material with an aqueoussolution of silver nitrate. Little, if any, reaction should take placein the absence of light. On subjecting the test mixture to light such asultraviolet light along with a control solution of silver nitrate, therate of darkening of the test solution compared to the control solutionis determined; if faster than the control solution, the test material isa photoconductor.

The photographic media comprise the photoconductor or an inert carriersheet which comprise any suitable backing of sufficient strength anddurability to satisfactorily serve as a reproduction carrier. Thecarrier sheet may be in any form such as, for example, sheets, ribbons,rolls, etc. The sheet can be made of any suitable material such as wood,rag content paper, pulp paper, plastics, e.g., polyethyleneterephthalate and cellulose acetate, cloth, metallic foil such asaluminum foil, and glass. The preferred form of the carrier sheet is athin sheet which is durable and flexible.

The photoconductor is normally applied to the carrier with a bindingagent. In general, these binders are translucent or transparent so thatthey do not interfere with transmission of light therethrough. Preferredbinder materials are organic materials such as resins, e.g.,butadienestyrene copolymers, poly (alkylacrylates) such as poly(methylmethacrylate), polyamides, polyvinyl acetate, polyvinyl alcohol andpolyvinylpyrrolidones.

Other photographic media containing other photosensitive components thanthe aforementioned which are developed with physical developers areuseful in this invention, for example, systems in which thephotosensitive component is a diazonium salt or a diazosulfonate asdescribed in the US. Pat. Nos. 2,183,447 and 2,750,292, respectively.

The exposure of the photographic medium can be by any of theart-recognized procedures such as described in the U.S. Patents andBritish Specification mentioned herein.

The new silver complex of the present invention is preferably formed insolution from a source of silver ions and a source of nitrilotriacetateions. Suitable sources of the respective ions are readily known in theart and the selection of any particular source is a matter of choice andgenerally one of convenience. The most preferred source of silver ion issilver nitrate because it is readily available and constitutes the mostcommon form. In addition, the solubility properties of silver nitratemake it eminently suited for the preparation of solutions of a widerange of concentrations. Other sources of silver ion can be used, evensilver ion complexes which are not as stable as that of the presentinvention but no appreciable advantage is realized, for which reason,the nitrate salt is usually preferred. The complexing ion,nitrilotriacetate ion, can be formed in solution by dissolving anysuitable source of the ion. Since the free acid itself is notappreciably dissociated in solution, it does not constitute a suitablesource of the required ion. Preferably, a soluble salt ofnitrilotriacetic acid is used as a source of the ion. Because of theirhigh solubility in water and aqueous solvent systems, the preferredsalts are ammonium and alkali metal salts (Na, K, Li), especially thesodium salts whichare commercially available. Since the complex ing ionis from a tribasic acid, it is possible to use each of the carboxylgroups for salt formation. Thus, it is possible to use, for example, thedisodium as well as the trisodium salt. The reason for preference of theammonium or alkali metal salts is the well known solubility of the mostsuch salts regardless of the negative ions present in solution, e.g.,the negative ions of the silver ion source. In photographic processing,the preference for systems in which various components have good watersolubility is well-known to those skilled in the art and need not befully explored for the purpose of this disclosure. Thus, the selectionof sources of silver ions and nitrilotriacetate ions should be based atleast in part on the possibility of precipitate formation between forexample the negative ion of the source of silver ion and the positiveion of the source of nitrilotriacetate ions. However, even should thecombination of ions from the respective sources, or from any source,including the solvent system, result in precipitate formation, this canbe remedied by the mere expedient of separating the precipitate from theliquid phase, e.g., by filtration or centrifugation and decantation. Ofcourse, the sources of the respective ions should be photographicallyacceptable, i.e., they should not adversely affect the photographicprocessing especially by establishing reactions competitive with thedesired oxidation-reduction reactions characteristic of photographicprocessing.

As an alternative to forming the silver nitrilotriacetate complex insolution for use in the hereindescribed process, it is possible butneedlessly tedious, to obtain a complex salt thereof, for example, byforming a supersaturated solution thereof, precipitating the complexsalt and separating the precipitate. No appreciable advantage isobtained by this procedure and because it entails considerabledifficulty it is generally avoided since the complex formed in solutionis useful as such. Additionally, if the complex salt were obtained bythe aforementioned procedure, it would of necessity be dissolved insolution for use in the described photographic processing.

When used in the form of a sensitizing solution for application directlyto the photographic latent image, results show that the concentration ofthe silver complex of this invention does not appear to be critical. Forexample, solutions containing as little as 10' moles per liter have beenused to sensitize latent images which on amplification gave excellentvisible prints corresponding to the original latent image.Concentrations ranging up to saturation concentration can be used, butthe preferred solutions are usually those of minimum concentration whichwill yield an effective latent silver image, for example from about 1X10to about 2X10 moles per liter, although concentrations as low as 1X10moles per liter are also operable. It is usually preferable to avoidhigher concentrations if the source of nitrilotriacetate is an alkalimetal salt due to the possible formation of silver oxide precipitate atextremely high pH values which result from such alkali metal salts. Whenthe higher concentrations are desired, it is preferred to use ammoniumslats or salts of weakly basic amines. The concentrations of therespective ions of the present new complex in solution need not beequimolar nor are they restricted to any specific stoichiometry sincethey may be varied appreciably in solution without adverse effect. As isobvious, too, the stoichiometry of the complex can also vary since thenegative ion is trivalent and silver ion is monovalent. Most likely ofthe'formulas of the complex ion is that in which one silver ion iscombined with one nitrilotriacetate ion, with the complex having aresidual charge of 2, especially when the sources of the respective ionsare used as equimolar concentration. There is no absolute requirementfor such equimolar concentration but it is usually preferred since bestresults are obtained therewith.

In lieu of using a solution of the present new silver complex, it ispossible to form the complex in situ by, for example, incorporating therespective sources of the ions in the photographic medium prior tophotoexposure, or alternatively, the source of nitrilotriacetate can beincorporated in the photographic medium prior to photoexposure and themedium contacted with silver ions after photoexposure. A furtherembodiment involves application of the nitrilotriacetate ion source inthe developer of the subsequent physical development processing. Whenreference is made in this disclosure and in the appended claims toconverting a photographic latent image to a latent silver image bycontacting the latent image with silver ions in the presence ofnitrilotriacetate ions, all of the foregoing embodiments are intendedthereby.

Of these embodiments, the preferred is the photographic medium,especially that comprising a photoconductor, containing the source ofnitrilotriacetate ions, with or without a source of silver ions. Thesaid sources of ions can be applied together to form the complex on thephotographic medium, or the respective sources can be maintainedseparately on the photographic medium, e.g., in microencapsulated formor in separate layers on the medium. When in separated form thephotographic media are activated after photoexposure by pressuring themicroencapsulated form or by merely exposing the medium to a solventsystem which permits reactive contact of the respective ions to form thenew silver complex. On activation, the complex then forms the latentmetal image which is then subjected to further processing to produce avisible image. When the medium contains a source of only one of the ionsof the new silver complex, the medium is activated after photoexposureby contacting with a solution of the other ion to form the desiredcomplex.

If desired, the photographic media can contain other materials such asthe developer and/or metal ions for the physical development processingsteps which follow latent silver image formation. For example, themedium can contain any of the aforementioned amplifying metals, e.g.,silver ions, copper ions, or stannous ions, or the reducing agentstherefor. If desired, these additional materials can be present inseparate layers or microencapsulated form, which can be activated asdescribed for the formation of the new silver complex of this invention.

In the foregoing description relative to inclusion of the new silvercomplex components and the said other materials, the preferred media arethose comprising a photoconductor as the photosensitive component,preferably titanium dioxide.

After the formation of the latent silver image, the medium is thensubjected to treatment with any of a variety of physical developersystems to obtain a visible image. The physical developers include thefollowing:

A. Silver physical developer:

1. Silver ion, e.g., silver nitrate;

2. Reducing agent for silver ion, e.g., N-(p-hydroxyphenyl glycine;N-methylaminophenol; ethylenediamines; hydroquinone; methylhydroquinone;ferrous compounds such as ferrous ethylenediaminetetraacetic acid andthe like;

3. fixer for silver ion, e.g., thiosulfate or thiocyanate salts.

B. Copper physical developer:

l. Copper ions, e.g., cupric or cuprous ion 2. a reducing agent forcopper ions, such as ascorbic acid, titanous and vanadous ion, andcomplexes of ferrous, titanous or vanadous ion with basicnitrogen-containing organic polycarboxylic acids, e.g., nitrilotriaceticacid, ethylenediaminetetraacetic acid and similar such acids. C.Stannous physical developer:

1. stannous ions 2. a reducing agent fro stannous ions, e.g., chromousions.

The additional silver ions of the silver physical developer may alreadybe present on the medium from the sensitizing step with the new silvercomplex of this invention. In most cases it is preferred to addadditional silver ion in the physical developing process but this is notalways necessary.

If desired, prior to physical development, the latent silver image canbe contacted with a reducing agent for silver which results in someamplification thereof with silver, the excess silver ion of thesensitizing solution being the source of reduced silver. The latentsilver image can thus become at least partially visible.

When the amplifying metal is other than silver, it is preferable toremove substantially all traces of silver ion from the medium prior tophysical development. When the initial sensitizing bath of the presentnew complex is of a low order concentration, e.g., less than molar, suchremoval is not always necessary. The removal can be by standardprocedures, such as water-washing or complex formation, e.g., withthiosulfate ion.

Conveniently, thiosulfate ion can be included in the amplifying metalion solution or in the reducing agent solution, thus obviating the needfor a separate treatment step.

When the copper physical developer is used, it is preferred to use asolution of cupric ethylenediaminetetraacetic acid or cupricnitrilotriacetic acid as the copper source and a solution of titanousethylenediaminetetraacetic acid or titanous nitrilotriacetic acid.

A further improvement in the overall processing to a visible amplifiedimage is realized when a source of nitrilotriacetate ions is included inthe solution of the reducing agent of the silver physical developer.

The principal improvements realized in the use of present new silvercomplex is an overall improvement in the apparent photographic speed ofthe photographic media treated therewith. The reason for the improvementis not necessarily fully understood, but seems to derive from a moreefficient utilization of the original radiation activated sites of themedium in the formation of the silver latent image which is discussedhereinbefore. The applicant does not wish to be bound by the theoreticalexplanation, but is seems quite logical for the purpose of explainingthe observed effects, as illustrated herein.

Additional advantage of the present new silver complex is the fact thatit functions at extremely low silver concentrations where, in theabsence of nitrilotriacetate ions, no detectable latent image is formed,or at best the latent image and the subsequently intensified image areweak, i.e., low density. The use of low concentrations of silver iongives an obvious economic advantage, and, even further, also givesexcellent results with a substantial reduction in the fog level of thedeveloped photographic medium.

These desirable effects are apparently peculiar to the present newcomplex and are not shared by analogous complexes. For example, whennitrilotriacetate ion if replaced by ethylenediaminetetraacetate ions,the resulting complex is found to be even less effective than simplesilver ion in solution in formation of the silver latent image; in manyinstances, no appreciable reduction of silver occurs from this complexon exposure to the photographic latent image, as evidenced by the lackof a visible image on physical development, or at best production ofonly a faint image.

In addition to its use in formation of silver latent images, the presentnew complex can also be used as a source of silver in electroplatingbaths and electroless plating baths, as a bacteriostat and for medicalpurposes for which silver nitrate is commonly used. In these uses, thecomplex is employed in the form of a solution, generally an aqueoussolution.

EXAMPLE 1 A sheet of paper coated with titanium dioxide (as described inBritish Specification 1,043,250) is exposed for 10 seconds on asensitometer. After a 10 second wait, the sheet is immersed for 10seconds in a solution which is 0.005 M silver nitrate and 0.005 Mtrisodium nitrilotriacetate and drained for 5 seconds. The paper is nextimmersed for 10 seconds in 200 ml. of a solution which is 0.48 M CuEDTAand 0.02 M sodium sulfite, mixed with ml. of a solution containing 2.0g./l. pmethylaminophenol and 7.5 g./l. Na SO and drained for 5 seconds.The paper in next immersed for 15 seconds in a solution of TiEDTA whichis 2.5Xl0' M thiourea (TiEDTA developer) and drained for 5 seconds toobtain a visible image of good density and contrast.

The TiEDTA solution is prepared by adding 10 ml. of 20 percent titanouschloride solution to a solution of 25 ml. of l M Na EDTA in 75 ml. ofwater.

Examination of stepwedges so prepared gives the following results.

Optical Density Sample Nos, otsteps step 21 stepgg step I l Fog. A ii+1.30 T30 1.03 0.18 B 21+ 1.30 1.28 1.02 018 C 21+ 1.28 1.25 0.95 0.15

For comparison, stepwedges prepared in the same manner but withoutnitrilotriacetate ions in the silver ion solution using show an averageof l 8 steps, and a somewhat lower density.

EXAMPLE 2 EXAMPLE 3 The procedure of Example 2 is repeated but the NaNTA at -a 0.003 M concentration is present in the silver nitratesolution. The results show an increase of 2 steps over the print ofExample 2, the total number of steps being 21.

EXAMPLE 4 EXAMPLE 5 Titanium dioxide-coated sheets are exposed for 10seconds held for 10 seconds and processed according to the followingprocedures:

Procedure A 1. Immerse for 10 seconds in a solution of:

A No, (0005M) 1M m m's.

and drain for 10 seconds. 2. Immerse for 30 seconds in the CuEDTAsolution containing silver developer described in Example 1. Procedure BIdentical with Procedure A but the silver ion concentration is 0.0025 Mand contains only 5 drops of 1 M Na NTA. Samples processed by thisprocedure have less fog than those processed by procedure A.

EXAMPLE 6 Titanium dioxide coated sheets are exposed for 3 seconds on aprint box to line negative and held for 10 seconds. The sheets are thenimmersed for 10 seconds in 0.0005 M AgNO which is 0.001 M Na NTA anddrained for 5 seconds. The sheets are then immersed for 15 seconds inthe following solution:

1M CuSO, 20 ml. IM CuEDTA 20 ml.

developer (Ag) 5 ml. H 55 ml.

Developer (Ag) is a solution of p-methylaminophenyl (2g./l.) and N2150:, (7.5g./l.). After draining for seconds, the sheets are immersed inTiEDTA developer (described in Example 1) for 5 seconds and washed for 5seconds.

The images are of excellent density and high contrast.

EXAMPLE 7 Titanium dioxide coated sheets are exposed for 3 seconds on aprint box, held for seconds, immersed for 10 seconds in 100 ml. of0.0005 M AgNO which contains 2.5 ml. 1M Na NTA and drained for 5seconds. The sheets are then immersed for seconds in 0.3 M CuEDTA(prepared with CuSO,) and drained for 5 seconds and then developed inTiEDTA developer (described in Example 1) for 5 seconds and finallywater washed. The prints obtained are of excellent density.

When this procedure is repeated omitting the Na NTA from the silver ionsolution, the prints obtained are of lower density then those producedwith Na NTA present in the silver ion solution.

EXAMPLE 8 Samples of a titaniumdioxide-coated paper are exposed on asensitometer (stepwedge) for 10 seconds and developed ac- 5 cording tothe following procedures:

A. l. immerse in 0.005 M AgNO for 10 seconds and drain for 10 seconds.2. develop in a solution of pmethylaminophenol (2g./l.)

and Na sO ('7.5g./l.).

l0 3. fix in aqueous Na S O for 1 minute and wash for 5 minutes. B. Sameas procedure A but 5 ml. of l M Na NTA is added per 100 ml. of AgNosolution. 15 Using Procedure A, the stepwedges show 15 steps for each oftwo sample sheets and with procedure B, two samples show 19 and 21 stepsrespectively.

When ethylenethiourea is added to the developer solution the number ofsteps increase.-

The procedures A and B are used with sample sheets exposed for 10seconds with similar results, Procedure A sheets showing 4 steps, whileProcedure B sheets show eight steps.

Procedures A and B are repeated with sheets exposed for 10" seconds butthe silver nitrate concentration is increased to 0.03 M. The procedure Asheets show 7 steps while Procedure B sheets show 9 steps.

EXAMPLE 9 Titanium dioxide coated sheets are exposed on a print box for3 seconds, held for 10 seconds and processed by the following sequence:

a. immerse for 10 seconds in 0.002 M AgNO containing 4 ml. of l M. NaNTA per 100 ml. and drain for 10 seconds.

b. develop for 30 seconds in solution of pmethylaminophenol (4g./l.)containing 6 ml. of l M 40 Na NTA per 100 ml. and drain for 10 seconds.

c. immerse in Na S O aqueous solution for 1 minute and water wash. Theprint shows 19 steps. When Na NTA is omitted from the silver nitratesolution and the developer, the print shows 13 steps.

EXAMPLE 10 Titanium dioxide coated sheets are exposed on a sensitome- 5Oter (stepwedge), held for 10 seconds and processed according to thefollowing sequence:

a. immerse for 10 seconds in'0.002 M AgNO containing 4 ml./ 100 ml. of lM Na NTA and drain for 10 seconds. b. immerse for 15 seconds in asolution composed of:

lM cuso. 20 ml.

lM m an 20 ml.

Solution of p-methylaminophenol (8 g./l.) 50 ml. H10 5 ml.

and drain for 10 seconds. c. develop for 10 seconds in TiEDTA developer(described in Example 1) and drain for 10 seconds. With an exposure timeof 10' seconds, the sheet shows 19 steps, with optical densities rangingfrom 1.09 to 0.82 (1 1th step).

When the immersion times are altered to (a) 5 seconds (b) 10 seconds and(c) 5 seconds and the drain periods to 5 seconds each, the sheet shown21 steps with the same optical .75 densities as the first sample, butwith lower background fog.

EXAMPLE 11 EXAMPLE 12 The procedure of Example 10 is repeated using thefollowing solution in step b:

l M. CuEDTA (prepared with 30 ml.

Cupric nitrate) 1M CuSO 10 ml.

developer(Ag) (described in 15 ml.

Example 6) H,O 45 ml.

The sheets show 21 steps with higher optical densities (1.21 for step 21and lower fog.

When 5 ml. of 1 M Na NTA is added to the copper solution,

the optical densities of the steps increase.

EXAMPLE 13 Titanium dioxide coated sheets are exposed on a sensitometer(stepwedge), held for 10 seconds, and processed according to thefollowing sequence: 5

a. immerse for 10 seconds in 0.001 M Ag SO containing 50 ml. 1M Na NTAper liter and drain 10 seconds. b. immerse for 10 seconds in a solutioncomposed of:

1M CuEDTA (from cupric 30 ml.

Nitrate) 1M CuSO 10 ml.

Dcveloper (Ag) (described 10 ml.

in Example 6) H 50 ml.

and drain 10 seconds. c. develop for seconds in TiEDTA developer(described in Example 1) Samples exposed for seconds showed 18 steps, D,,,==l.ll and fog=0.l 1.

Sheets exposed to continuous tone negatives for 10' seconds areprocessed using this procedure to obtain excellent prints of goodresolution.

EXAMPLE 14 Titanium dioxide coated paper sheet are exposed on a printbox to a line negative for 3 seconds and processed according to thefollowing sequence:

a. immerse for 10 seconds in 0.0001 AgNO containing 2.5 ml. of 1 M NaNTA per 100 m1. of solution and drain for 10 seconds.

b. immerse for 30 seconds in developer (Ag) (described in Example 6) anddrain for 10 seconds.

0. immerse for 30 seconds in 0.25 M CuSO and drain for 10 seconds.

d. develop for 30 seconds in TiEDTA developer (Example 1 and water wash.

The prints obtained are of good density and contrast. When the silvernitrate concentration is increased to 0.0005 M, prints of better densityare obtained.

EXAMPLE 15 The prints show a good, black image corresponding to thenegative.

EXAMPLE 16 The procedure of Example 10 is repeated using a solution of0.5 M stannous chloride which is also 3.5 M NaClin lieu of the copperamplifying solution. As reducing agent for stannous, a solution ofchromous chloride (0.5 M) containing 2g./l. of glue and 0.3g./1. cresolis used. The developing time is a 30 seconds immersion in the reducingagent.

The stepwedge shows 18 steps and D ,,,=0.74.

EXAMPLE 17 The procedure of Example 10 is repeated excepting that thesource of nitriloacetate ions (Na NTA) is applied to the photosensitivemedium prior to photoexposure by immersion for 30 seconds in a 1 Msolution of trisodium nitrilotriacetate, with equivalent results.

EXAMPLE 18 The procedure of Example 1 is repeated with thephotosensitive medium being sensitized with the solution of silvernitrilotriacetate complex ion prior to photoexposure. Comparable imagesof good density and contrast are obtained.

EXAMPLE 19 The procedure of Example 7 is repeated using the followingtreating steps:

1. immerse (after 10 seconds photoexposure) for 10 seconds in 10 M.silver nitrilotriacetate complex ion solution and drain for 10 seconds.

2. immerse in a solution of p-methylaminophenol (2g./l.) and Na SO(7.5g./1.) for 30 seconds and drain 10 seconds.

3. immerse for 30 seconds in 0.5 M SnCl which is also 3.0 M NaCl andcontains 5 ml. conc. hydrochloric acid/liter and drain for 10 seconds.

4. immerse in freshly prepared 0.25 M chromous chloride in l M sulfuricacid solution for 30 seconds and then water wash.

An image of comparable density and contrast is obtained.

In the foregoing examples, the photosensitive media are principallypaper and plastic film coated with the photoconductor. Similar resultsare obtained with metal foil coated with titanium dioxide, such asaluminum sheets coated with titanium dioxide, e.g., as described incommonly assigned copending [1.8. application Ser. No. 446,707 filedApr. 8, 1965, now abandoned.

EXAMPLE 20 A subbed triacetate film is coated with gelatin layercontaining trisodium nitrilotriacetate. The dried layer is then coatedwith T10 in gelatin and dried. The medium is then imagewise exposed tolight, immersed for 10 seconds in 0.00119 silver nitrilotriacetic acid,developed in a solution of pmethylaminophenol (2g./l.) and Na SO(7.5g./1.) for 15 seconds and then amplified with 0.25 M CuSO, andTiEDTA developer solution as in the previous examples.

EXAMPLE 21 An anodized aluminum plate is coated with an aqueous slurryof TiO and polyvinyl alcohol and the coating dried. The medium isimagewise exposed to light and immersed for 10 seconds in 0.001 M AgNTAfollowed by development in pmethylaminophenol and Na S0 as in Example21. The medium is then amplified using steps (c) and (d) of Example 15.

EXAMPLE 22 A subbed triacetate film is coated with solution of CuEDTA ina suitable binder and dried. The coated medium is then coated with aslurry of Ti0 and AgNTA complex in a suitable binder and dried in theabsence of air. The medium is then exposed imagewise to light,optionally developed in a solution of p-methylaminophenol (2 g./l.) andNa SO (7.5 g./l.) and then immersed in titanous nitrilotriacetatedeveloper for 30 seconds as in the previous examples to obtain an imageof good density.

In addition to amplifying photographic images as described in theforegoing examples, the present systems and processes are also useful inthe production of printed circuits as described in commonly assignedcopending US. applications Ser. Nos. 721,778, filed Apr. 16, 19 68 and717,502 filed Apr. 1, 1968.

In the foregoing disclosure and in the attached claims, reference to thevarious metal complexes by use of conventional names, e.g., titanousnitrilotriacetic acid, ferrous ethylenediaminetetraacetic acid, silver'nitrilotriacetic acid and the like, is intended to denote the complexion made up of the indicated metal ion and an ion corresponding to theindicated acid. As is obvious to anyone skilled in the art, thestoichiometry of the complexes is not necessarily a simple 1:1 ratio butmay vary somewhat according to the relative concentrations of therespective ions in solution. Since these complexes are formed readilyfrom relatively soluble sources of the respective ions in solution andthe additional ions of these sources in the solution do not adverselyaffect the formation of the desired complex, nor are they appreciablyreactive in the oxidation-reduction reactions involving the desiredcomplex, there is no need to designate the additional ions whenreferring to the complex. Of course, the additional ions are thoseremaining in solution and not involved in the complex formation, e.g.,alkali metal ions, such as sodium or potassium ions,

is as given in Stability Constants of Metal-ion Complexes, L. G. Sillenand A. E. Ma'rtell, Special Publication No. 17, The Chemical Society,London. The effect of complexation on the Ag, Ag potential can beestimated by substituting the Ag* concentration obtained from theformation constant into the Nernst equation:

[Ag EDTA [Ag EDTA or ammonium ion from the source of complexing acid,and the Y negative ion of the metal salt introduced, e.g., sulfate,nitrate, halide and the like. Thus, the designation of the complexes bysuch expressions as titanous nitrilotriaeetic acid, ferrousethylenediaminetetraacetic acid and the like is intended to embrace thecomplex ions in solution, irrespective of the source of the respectiveions which made up the complex. As mentioned hereinabove and as anyoneskilled in the art will appreciate, the source of the respective ionsshould not contain ions which would adversely affect formation of thedesired complex ion or adversely affect the oxidation-reduction reactionnecessary for image amplification. Preferably, the selection .of suchion sources should not result in precipitate formation between thenegative ion of the metal ion source and positive ion for the complexingacid ion source. Thus, the salt of the complexing acid is preferably analkali metal or ammonium slat both of which form soluble salts with mostnegative ions. In other words, the sources of silver ion andnitrilotriacetate ion, respectively, as well as the solutions thereofused in the photographic-development process used herein should containonly ions which are photographically acceptable and the environment inwhich they are employed should be photographically acceptable.

The following data is provided to illustrate the existence of the newsilver complex of this invention:

Potential measurements were made on a solution of Ag and NTA to showthat complex formation occurred between these two ions. Some preliminarypotential measurements were made on solutions whose potentials could beestimated. The potential of a 0.005 M AgNO solution can be calculatedfrom the Nernst equation to be 1f the potential of this solution ismeasured against a saturated calomel electrode with an Ag electrode, theE cell valve should be 0.663 0.244=0.4l9 V. A measured B cell of 0.425V. was obtained for 0.005 M AgNO at pH 5.9 versus the saturated calomelelectrode.

The effect of EDTA' 'on the Ag, Ag potential was determined in view ofthe fact that EDTA is known to form a complex with Ag The equilibriumconstant for the reaction,

This 0.367 V. is the new half-cell potential, E for the halfreaction,

Ag EDTA +e=Ag+EDTA" at a unit concentration ratio of the variablespecies. As a result of this formulation, and since the Ag EDTA"concentration is in the new Nernst equation, the reduction of the AgEDTA- complex itself is being considered. At a unit concentration ratioof [Ag EDTA]/[EDTA a calculated E cell of 0.3670.244 =E" V. is obtainedversus the saturated calomel electrode. A 0.005 M AgNO 0.010 M Na, EDTAsolution was prepared. The solution was clear, colorless and at pH 10.6.If complexation occurs to any appreciable extent in this solution, theconcentration of the complex should be close to 0.005 M and the freeEDTA should also be near 0.005 M and thus the ratio of species should beclose to unity. The E cell for this solution was 0. l 69 V. versus thesaturated calomel electrode. This value does not disagree to any greatextent with the calculated 0.123 V. It was also found that a 0.005 MAgNO solution cannot remain soluble above pH 9.0 without precipitatingout as the oxide. These two observations confirm that a soluble Ag EDTAcomplex exists in a somewhat alkaline solution.

A 0.005 M AgNO 0.010 M Na NTA solution was prepared. A clear, colorlesssolution of pH 10.6 was obtained. The E cell of this solution versus thesaturated calomel electrode was 0.252 V. The value of the half-cellpotential, E, versus the normal hydrogen electrode is 0.252+0.244=0.496V. The reduction reaction for the complexed species is:

and the corresponding Nernst equation is:

If it is assumed that the concentration ratio [AgNTA ']/[NTA is close tounity, then the measured E vs. the normal hydrogen electrode is equalapproximately to E. This E is related to an analogous way to theformation constant of AgN- TA as the E for Ag EDT/X Thus,

E=E0.059 log K, AgNTA O.496=0.799-0.059 log K 0.496+0.799 .liiffiy f--jw-0059. 7 1 and This last value is the same as that for a 0.005 M AgNOwithout any complexing agents present. This indicates that the portionwas displacing the complexed Ag The foregoing results indicate that atalkaline pHs, NTAWorms a complex with Ag having a relatively smallformation constant as compared to the formation constants of NTA withother metal ions.

What is claimed is:

1. In the method of rendering visible a latent image of animagewise-exposed medium comprising a radiation-activatablephotoconductor by converting said latent image to a silver latent imageand amplifying said silver latent image with'a physical developer, theimprovement comprising:

contacting said exposed medium with a sensitizing solution containingsilver ions in the presence of nitrilotriacetate ions, said solutionhaving a pH of above about 4.

2. An improvement of claim 1 wherein said sensitizing solution comprisesan aqueous solution having a concentration of silver nitrilotriacetatecomplex of from about l lO" to about 2X l O'moles per liter.

3. An improvement of claim 1 wherein said physical developer containssilver ions and a photographic reducing agent for silver ions.

4. An improvement of claim 1 wherein said physical developer containscopper ions and a reducing agent for copper ions.

5. An improvement of claim 1 wherein said physical developer containstin ions and a reducing agent for tin ions.

6. In the method of rendering visible a latent image of animagewise-exposed medium comprising a radiation activatablephotoconductor with a developer composition, the improvement comprising:

contacting said exposed medium with a solution comprising a complex ofsilver nitrilotriacetate.

7. An improvement of claim 6 wherein the concentration of said silvernitrilotriacetate complex is from about 1X10". to about 2X10" moles perliter.

8. A photographic medium containing a radiation-activatablephotoconductor of titanium dioxide on zinc oxide as the photosensitivecomponent thereof and a source of nitrilotriacetate ions.

2. An improvement of claim 1 wherein said sensitizing solution comprisesan aqueous solution having a concentration of silver nitrilotriacetatecomplex of from about 1 X 10 5 to about 2 X 10 1 moles per liter.
 3. Animprovement of claim 1 wherein said physical developer contains silverions and a photographic reducing agent for silver ions.
 4. Animprovement of claim 1 wherein said physical developer contains copperions and a reducing agent for copper ions.
 5. An improvement of claim 1wherein said physical developer contains tin ions and a reducing agentfor tin ions.
 6. In the method of rendering visible a latent image of animagewise-exposed medium comprising a radiation activatablephotoconductor with a developer composition, the improvement comprising:contacting said exposed medium with a solution comprising a complex ofsilver nitrilotriacetate.
 7. An improvement of claim 6 wherein theconcentration of said silver nitrilotriacetate complex is from about 1 X10 5 to about 2 X 10 1 moles per liter.
 8. A photographic mediumcontaining a radiation-activatable photoconductor of titanium dioxide onzinc oxide as the photosensitive component thereof and a source ofnitrilotriacetate ions.